Microphone with carbon electrodes



9 E. scl-uRcKs 2,572,525

MICROPHONE WITH CARBON ELECTRODES Filed July 29, 1948 2 SHEETS-*Sl-IEET l INVENTOR Erich Schircks.

ATTORNEY Oct. 23', 1951 E. SCHIRCKS k 5 9 MICROPHONE WITH CARBON ELECTRODES Filed July 29, 1948 2 SHEET-SHEET 2 BNVENTOR.

Erich Schimks.

ATTORNEY Patented Oct. 23, 1951 MICROPHONE WITH CARBON ELECTRODES Eric Schirc cs Zurich, Switzerland, assignor to Alb swerk Zuerich A. G., Zurich, Switzerland,

a Swiss company Application July 29, 1948, Serial No. 41,371

p In Switzerland August 6, 1947 3 Claims. (Cl. 179-424) The invention relates to carbon microphones,

particularly to microphones in which a conical electrode is conductively secured to a diaphragm and influences the granulated carbon contained in a funnel electrode insulatingly secured to the microphone housing.

The aim if the invention is to improve such microphones as regards sensitivity, stability of operating properties and evenness of frequency characteristics.

To this end, and in accordance with a feature of the invention, a carbon microphone has a funnel electrode provided with groove-like depressions that extend in the direction of the contour lines (generatrices) of the funnel surface. According to another feature of the invention, the space between the diaphragm and the back of the housing is divided into two chambers by a partition which is perforated in addition to the central aperture necessary for the passage of the diaphragm electrode.

These and other features of the invention are apparent from the embodiment shown in the drawing in which Fig. 1 is a diametrical cross section of a microphone according to the invention, and Fig. 2 an exploded perspective view of its individual components.

The diaphragm I of the microphone consists, for example, of an aluminum foil and has a conical electrode 2 conductivel cemented thereto. The rigid portion of the microphone housing 3 carries a funnel electrode 4. Insulatin washers 4|, 42 and metal components 43, 44 serve to fasten the funnel electrode. An insulating member 45 has a bore for the passage of the connection leads of the microphone. The funnel surface of electrode 4 has groove-like depressions 46 extending along contour lines (generatrices) of that surface. The upper portion 41 of the funnel surface is rendered non-conducting by the application of a coat of insulating varnish. An intermediate wall 5 partitions the space between diaphragm I and the back of the housing 3 and has a central opening 5| for the conical electrode 2 and further perforations 52 arranged on a circle concentric to opening 5|. These perforations are covered by a felt ring 6. A second felt ring 6| is inserted to improve the sealing of the funnel electrode, i. e. to prevent the escape of the carbon granules disposed between the two electrodes. A protective lid 32 has sound holes 33 arranged in a concentric circle. A spacing ring 34 separates the diaphragm I from the partition 5. A flanged ring 35 holds the entire microphone together.

The groove-shaped depressions in the direction of the contour lines of the surface of the funnel electrode perform the function of carbon granule storage chambers and control the flow of the granules between the two electrodes. Due to acoustical or mechanical vibration, the detrimental interruption effect otherwise occurring because of the adhesion of the granules at individual points when the microphone has been switched out of circuit, is remedied and the full sensitivity of the microphone restored. Microphones with electrodes designed in this manner require smaller carbon granules than those of the special, for instance star-shaped, carbon-granules pot already proposed for the known types of microphone. The perforated partition which subdivides the space between the diaphragm and the back portion of the housing into two chambers of limited inter-communication serves the purpose of providing, with the aid of the perforations, a damping effect operative only on a particular frequency band. This is possible because the additional apertures 52 are so dimensioned that they are not operative in a low-frequence region. That is, no effective air friction is encompassed for these low frequencies at the apertures, while for higher frequencies these apertures act as a closed wall. The most favorable size for these apertures is determined by tests. The procedure is such that with a minimum of apertures 52 indicated by experience, the frequency course of the microphone is determined, whereupon, according to the result, the apertures are enlarged until the frequency course complies with requirements. The felt ring 6 on the one hand prevents the carbon granules from escaping and on the other hand covers the apertures in the intermediate wall, thereby subdividing them into a large number of small apertures. The conical electrode may be cemented to the diaphragm with the aid of some conductive substance. For this purpose an in itself non-conducting cement can be mixed with, for instance, carbon dust.

I claim:

1. A microphone, comprising a housing, a diaphragm mounted on said housing, a conical electrode secured to said diaphragm, a funnel electrode secured to said housing and having a funnel surface coaxial with and spaced from said conical electrode, said funnel electrode having grooves in said surface extendin from the funnel point toward the funnel periphery, and carbon granules between said grooved surface and said conical electrode.

2. A microphone, comprising a. housing, a, di-

aphragm mounted in said housing, a conical carbon electrode conductively secured to said d1- aphragm, a funnel electrode insulatedly secured to said hOuSing opposite said conical electrode and having a funnel surface substantially con- 5 centric to, and spaced from said conical electrode, said funnel ielectrode 'having grooves; in said surface extending substantially along respective contour lines of said surface, and carbon granules between said grooved surface and isaid conical electrode. 551,588 3. A microphone, comprising a housing, a"dia-' 5 3 395 phragm mounted on said'housing, a; partition 77 409 extending within said housing'rand-dividing it 11 1 7 231 into two chambers of which one is bordered by 15 2,140,859 said diaphragm, said partition. having-a central. 2 149 23 opening and additional erforations, a conical ;2' .1'7-9, 733 electrode secured to said diaphragm and extend- 2 435 920 ing through said central opening into: the other chamber, a funnel electrode mounted in said 20 1 other chamber coaxially with: said conicalelecvNumber :trode and havin -funnel surfacegrooved. generatrix? directions, carbon granules betweensaid electrodes, and a felt ring surrounding said open-'- ing and covering said perforations.

ERICH SCHIRCKS.

REFERENCES CITED The following references are of record in the file of" this patent:

UNITED STATES PATENTS Name Date Lockwood Apr. '7, 1896 Moore July '7, 1896 .Frykman Dec. 27, 1904 Palmer Nov. 1'7, 1914 M Sold'an Dec. 20, 1938 Eye Mar. 7, 1939 Sutton Nov. 14, 1939 Burroughs Feb. 10, 1948 FOREIGN PATENTS Country 7 Date- 2 Great. Britain. .Oct. 5, 19.39 

